The Orinoco is one of the longest rivers in South America at 2,140 kilometres (1,330 mi). Its drainage basin, sometimes called the Orinoquia, covers 880,000 square kilometres (340,000 sq mi), with 76.3 percent of it in Venezuela and the remainder in Colombia. The Orinoco and its tributaries are the major transportation system for eastern and interior Venezuela and the llanos of Colombia. The Orinoco is extremely diverse and hosts a wide variety of flora and fauna.

The first powerline crossing of the Orinoco was completed in 1981 for an 800kVTL single span of 1,200 metres (3,900 ft) using two towers 110 metres (360 ft) tall.[4] In 1992, an overhead power line crossing for two 400kV-circuits was completed just west of Morocure (between the cities of Ciudad Bolivar and Ciudad Guayana), north of the confluence of Routes1 and 19. It had three towers, and the two spans measured 2,161 metres (7,090 ft) and 2,537 metres (8,323 ft), respectively.[4][5][6][7]

The course of the Orinoco forms a wide ellipsoidal arc, surrounding the Guiana Shield; it is divided in four stretches of unequal length that roughly correspond to the longitudinal zonation of a typical large river:

Upper Orinoco— 242 kilometres (150 mi) long, from its headwaters to the rapids Raudales de Guaharibos, flows through mountainous landscape in a northwesterly direction

Middle Orinoco— 750 kilometres (470 mi) long, divided into two sectors, the first of which ca. 480 kilometres (300 mi) long has a general westward direction down to the confluence with the Atabapo and Guaviare rivers at San Fernando de Atabapo; the second flows northward, for about 270 kilometres (170 mi), along the Venezuelan - Colombian border, flanked on both sides by the westernmost granitic upwellings of the Guiana Shield which impede the development of a flood plain, to the Atures rapids near the confluence with the Meta River at Puerto Carreño,

Lower Orinoco— 959 kilometres (596 mi) long with a well-developed alluvial plain, flows in a northeast direction, from Atures rapids down to Piacoa in front of Barrancas

Delta Amacuro— 200 kilometres (120 mi) long that empties into the Gulf of Paría and the Atlantic Ocean, a very large delta, some 22,500 km2 (8,700 sq mi) and 370 kilometres (230 mi) at its widest.

At its mouth, the Orinoco forms a wide delta that branches off into hundreds of rivers and waterways that flow through 41,000 km2 (16,000 sq mi) of swampy forests. In the rainy season, the Orinoco can swell to a breadth of 22 kilometres (14 mi) and a depth of 100 metres (330 ft).

Most of the important Venezuelan rivers are tributaries of the Orinoco, the largest being the Caroní, which joins it at Puerto Ordaz, close to the Llovizna Falls. A peculiarity of the Orinoco river system is the Casiquiare canal, which starts as an arm of the Orinoco, and finds its way to the Rio Negro, a tributary of the Amazon, thus forming a 'natural canal' between Orinoco and Amazon.

More than 1000 fish species have been recorded in the river basin.[9] Among these are species found in brackish or salt water in the Orinoco estuary, but also many restricted to fresh water. By far the largest orders are Characiformes and Siluriformes, which together account for more than half the fresh water species.[10] Some of the more famous are the black spot piranha and the cardinal tetra. The latter species, which is important in the aquarium industry, is also found in the Rio Negro, revealing the connection between this river and the Orinoco through the Casiquiare canal.[11]

In 1926 a Venezuelan mining inspector found one of the richest iron ore deposits near the Orinoco delta, south of the town of San Felix on a mountain name El Florero. Full-scale mining of the ore deposits began after World War II, by a conglomerate of Venezuelan firms and US steel companies. At the start in the early 1950s, about 10,000 tons of ore-bearing soil was mined per day.[12]

Since 1988, the local government of Ciudad Guayana has conducted a swim race in the rivers Orinoco and Caroní, with up to 1000 competitors. Since 1991, the "Paso a Nado Internacional de los Rios Orinoco-Caroní" has been celebrated every year, on a Sunday close to 19 April. Worldwide, this swim-meet has gained in importance, and it has a large number of competitors.[15]

Stark, James H. 1897. Stark's Guide-Book and History of Trinidad including Tobago, Granada, and St. Vincent; also a trip up the Orinoco and a description of the great Venezuelan Pitch Lake. Boston, James H. Stark, publisher; London, Sampson Low, Marston & Company. (This book has an excellent description of a trip up the Orinoco as far as Ciudad Bolívar and a detailed description of the Venezuelan Pitch Lake situated on the western side of the Gulf of Paria opposite.)

MacKee, E.D., Nordin, C.F. and D. Perez-Hernandez (1998). "The Waters and Sediments of the Rio Orinoco and its major Tributaries, Venezuela and Colombia." United States Geological Survey water-supply paper, ISSN0886-9308 /A-B. Washington: United States Government Printing Office.